(1) Field of the Invention
The present invention relates generally to chemical injection devices and, more particularly, to a co-axial chemical injection device using high-velocity gases.
(2) Description of the Prior Art
Combustion furnaces utilize injection of chemical reagents to reduce NOx and other noxious substances in the combustion effluent. These reagents are frequently dissolved in water and injected into the combustion space under pressure, forming water droplets that aid in the dispersion of the chemical reagents in the combustion gases.
In a low-relative humidity environment, the droplets will start evaporating before they have a chance to reach their boiling point. The droplets will therefore completely evaporate and make the reagent dissolved in the water droplets chemically available much sooner than the time required for the droplets to reach their boiling point. Making the reagent chemically available prematurely may lead to undesirable side reactions. In the case of NH3 and NH3-based reagents that are injected into combustion furnaces in order to react with NOx compounds to reduce them to elemental nitrogen, premature availability of the NH3 at elevated temperatures can cause them to be oxidized themselves to NOx, thereby actually raising the combustion gas NOx levels, rather than reducing them.
Prior art methods utilized large droplet sizes to delay the complete evaporation of the droplet and availability of the chemical reagent dissolved therein. However, in high-turbulence systems, droplet sizes are limited by the shear of the gases. Therefore, a need exists for a method to prevent complete evaporation of liquid droplets in a high-turbulence system until complete evaporation is desired.
Chemical injection devices are generally known. Example of some prior art devices include U.S. Pat. No. 5,342,592 issued to Peter-Hoblyn et al. on Aug. 30, 1994 for Lance-type injection apparatus for introducing chemical agents into flue gases teaches the removal of sulfur oxides (SOx) and nitrogen oxides (NOx) from combustion effluents is enhanced by the supplying of reactants in a particular distribution pattern in the gas flow. To achieve the particular distribution pattern and to avoid impingement of the reactant on the heat exchanger tubes of the combustor, an elongated injection lance comprising c cooling jacket and plural spaced injections ports is employed. The cooling jacket protects the reactant supply to the injection ports from the high temperatures of the combustion gases.
U.S. Pat. No. 4,985,218 issued to DeVita on Jan. 15, 1991 for Process and injector for reducing the concentration of pollutants in an effluent teaches a process and apparatus for reducing the concentration of pollutants in an effluent from the combustion of a fuel or waste material is presented. The process and apparatus enables injection of an effluent treatment fluid at low treatment fluid flow rates yet provides an even dispersion of treatment fluid within an effluent passage with little or no clogging. An atomization conduit, positioned coaxially within a treatment fluid supply conduit, extends into the effluent and supplies an atomization fluid, such as steam or air. A treatment fluid is supplied through a supply conduit and through at least one jet in the atomization conduit wall at a velocity of between 2-60 feet per second, causing atomization of the treatment fluid within the nozzle.
U.S. Pat. No. 4,915,036 issued to DeVita on Apr. 10, 1990 for Boiler and injector for reducing the concentration of pollutants in an effluent teaches a process and apparatus for reducing the concentration of pollutants in an effluent from the combustion of a fuel or waste material is presented. The process and apparatus enables injection of an effluent treatment fluid at low treatment fluid flow rates yet provides an even dispersion of treatment fluid within an effluent passage with little or no clogging. An atomization conduit, positioned coaxially within a treatment fluid supply conduit, extends into the effluent and supplies an atomization fluid, such as steam or air. A treatment fluid is supplied through a supply conduit and through at least one jet in the atomization conduit wall at a velocity of between 2-60 feet per second, causing atomization of the treatment fluid within the nozzle.
U.S. Pat. No. 4,842,834 issued to Burton on Jun. 27, 1989 for Process for reducing the concentration of pollutants in an effluent teaches a process and apparatus for reducing the concentration of pollutants in an effluent from the combustion of a fuel is presented. The process and apparatus enables injection of an effluent treatment fluid at independently variable droplet sizes and distance of injection to a wide variety of distribution patterns within an effluent passage. An atomization conduit, positioned coaxially around a treatment fluid conduit, extends into the effluent and supplies an atomization fluid. The supply conduit is axially slidable with respect to the atomization conduit and supplying a treatment fluid through the supply conduit. The relative axial position of supply conduit and the atomization conduit is adjusted and the rate of flow of the atomization fluid is selected to inject droplets of a size effective to a desired distance within the passage.
The use of urea and NH3-generating compounds is known in the prior art. Example of the use of urea and NH3-generating compounds include U.S. Pat. No. 4,992,249 issued Feb. 12, 1991 to Bowers for Reduction of nitrogen- and carbon-based pollutants through the use of urea solutions and U.S. Pat. No. 4,927,612 issued May 22, 1990 invented by Bowers for Reduction of nitrogen- and carbon-based pollutants teaches process using a dispersion of aqueous urea solution is injected into an effluent for reducing nitrogen oxides in an effluent from the combustion of carbonaceous fuel.
U.S. Pat. No. 5,057,293 issued May 22, 1990 invented by Epperly, et al. and assigned to Fuel Tech, Inc. for Multi-stage process for reducing the concentration of pollutants in an effluent teaches a process for the reduction of the concentration of nitrogen oxides in the effluent from the combustion of a carbonaceous fuel, the process comprising selecting a plurality of locations for introduction of chemical formulations and introducing at each of said locations at least one chemical formulation, selected from the group consisting of urea, ammonia, hexamethylenetetraamine, an oxygenated hydrocarbon, a paraffinic hydrocarbon, an olefinic hydrocarbon, an aromatic hydrocarbon, an ammonium salt of an organic acid having a carbon to nitrogen ratio of greater than 1:1, a hydroxy amino hydrocarbon, a heterocyclic hydrocarbon having at least one cyclic oxygen, a five- or six-membered heterocyclic hydrocarbon having at least one cyclic nitrogen, hydrogen peroxide, guanidine, guanidine carbonate, biguanidine, guanylurea sulfate, melamine, dicyandiamide, calcium cyanamide, biuret, 1,1′-azobisformamide, methylol urea, methylol urea-urea condensation product, dimethylol urea, methyl urea, methyl urea, and mixtures thereof, effective to reduce the concentration of nitrogen oxides at the effluent temperature existing at said location, such that optimization of the level of injection at each of said locations leads to the reduction of the level of nitrogen oxides below a predetermined target level.
U.S. Pat. No. 4,208,386 issued Jun. 17, 1980 to Arand, et al. for Urea reduction of NOx in combustion effluents and U.S. Pat. No. 4,325,924 issued to Arand, et al. on Apr. 20, 1982 for Urea reduction of NO.sub.x in fuel rich combustion effluents teach methods for reducing NOx in combustion effluents involving introducing urea into the combustion effluent.